What Causes Severe Itching In The Butt Crack?

I am a 30 year old mother of 3. Healthy, married, etc. For the past 2 days the top of my butt crack has been extremely and consistently itchy..no bumps etc...can not figure it out..the wEek before this happened I had been on vacation with my family and in a bathing suit a lot out by the pool?? Please help, the itching kept me up a lot last night!